ON THE BRITISH SPECIES OP OEISIA. 157 



refers, that he has united all these forms in a single species; 

 and adds, " Auctores vero si sequi volumus, unamquamque fere 

 coloniam speciem distinctam habebimus." 



Although not in the least denying the diflBculty of finding 

 satisfactory specific characters other than those derived from 

 the ovicells, the result of my investigation has been to con- 

 vince me that Smitt has gone too far in denying the specific 

 value of certain of the forms of Crisia. My results may 

 possibly have to be explained by a suggestion which Smitt 

 himself throws out, to the effect that although the series repre- 

 sented by the various forms of Crisia living in difi'erent locali- 

 ties is one in which practically none of the stages in the evolu- 

 tion of the species have been lost, " vivit multis in locis altera 

 vel altera forma tam constaus, ut species bene distincta facile 

 censeatur."^ Unfortunately, all the localities from which I 

 have been able to obtain Crisia are comparatively close to one 

 another ; but I have found no essential differences between the 

 forms of the same species from different localities. 



Until it can be shown that any two or more of these forms 

 can be developed as branches from the same stem, or as stems 

 from the same rootlet, or at least that they can be produced as 

 descendants of the same form, it appears to me that it will be 

 impossible to deny to them the rank of species. 



C. eburnea begins to breed at Plymouth as early as 

 February ; ovicells are present in great numbers during 

 March, April, and May. Towards the end of the latter month 

 they disappear, and are not normally present on colonies 

 found in the summer. March and April appear to be the 

 months when ovicells are most common. 



C. ramosa commences to breed (at Plymouth) in April; a 

 few of the colonies found at this period have young ovicells. 

 In May young ovicells are very common ; and the breeding 

 period continues from this time until August at any rate. 

 Immature ovicells may be found even at this time, but they 

 are then becoming uncommon. The breeding season is pro- 

 bably at its height in May and June. 



' ' Ofvers.,' &c., 1867, No. 6, p. 461. 



veil. V, PART II. 15 



